1. Field of the Invention
The present invention relates generally to the field of antifriction bearings and housings for such bearings. More particularly, the invention relates to a molded polymeric bearing housing including features advantageous in certain applications, such as in the food and beverage industries.
2. Description of the Related Art
A wide range of applications exist for antifriction bearings, such as ball bearings, roller bearings, needle bearings and the like. In many industrial and material handling systems, such bearings perform a fundamental function of permitting rotating machine elements to turn with little resistance and thereby to effectively transmit power and motion between drive system components. Applications for such bearings include conveyors, mixers, pump drives, and the like, to mention just a few.
In general, bearings of the type commonly used in most industries include an inner race, an outer race, and a plurality of antifriction bearing elements disposed therebetween. The bearing elements are captured by the races and permit the races to rotate freely with respect to one another. The bearing assembly is typically installed in and supported by a housing. A number of housing types are known and are in common usage, including pillow block styles, two and four bolt flanged styles, take-up frame styles, and so forth. In addition to supporting the bearing inserts, such housings include features that permit them to be easily attached to machine frames and other support structures at the application. Depending upon the housing style, these features typically include support feet or flanges traversed by apertures for receiving fasteners. Once mounted on the machine frame, a base surface of the bearing housing generally abuts the machine frame and forms a solid foundation for both the bearing insert and for the machine elements held in rotation by the bearing insert.
Housings of the type described above are commonly made of a variety of materials depending upon the particular application, the loads to which the bearing insert will be subjected and the environmental conditions of the application. For example, in most bearing styles, metal housings provide sufficient mechanical support and resistance to loads. However, such metal housings are not well-suited to certain applications. Specifically, in certain industries health or environmental constraints may make the use of metal bearing housings difficult or impossible. In the food and beverage industries, for example, health requirements often necessitate frequent washing of processing and material handling equipment including bearings and their housings. Under such conditions, conventional metal housings may tend to corrode or otherwise degrade in ways that would contaminate the working conditions of the machinery and/or the product processed by the machinery. Similarly, in chemical processing industries and certain marine applications the presence of corrosive substances may significantly reduce the life of conventional metal bearing housings. In response, the industry has began to employ alternative materials for bearing housings, including certain plastics.
In general, conventional plastic bearing housings are available in the same styles as their metal counterparts. Thus, pillow block bearing styles are available from various manufacturers which differ only slightly from designs available in metal. However, due to manufacturing and processing constraints unique to plastic materials certain features of conventional plastic bearing housings present drawbacks which make them unsatisfactory in specific industrial applications. For example, due to the particular geometry of some bearing housing styles, such as pillow block housings, large volumes of the housing may be present in regions of the housing, while relatively thin or small volumes are present in other regions. Due to the exigencies of conventional injection molding processes, most conventional designs therefore include ribbed structures in the larger volumes regions to provide the requisite structural integrity, while providing sufficient material flow and curing in those regions and avoiding drawing during the curing process. In pillow block designs, for example, ribs are commonly provided below the bearing support and the lower support flanges. Some or all of these ribs contact the machine frame when the housing is installed, leaving voids or cavities below the bearing housing between the housing and the machine frame. While the plastic housing itself may perform adequately under frequent and repeated washdowns, such interstices left between the housing and the machine frame tend to remain wet or moist. Over time, these areas tend to promote the growth of fungi, molds, bacteria and other microorganisms reducing the utility of the housing and requiring additional downtime for cleaning or even replacement of the housing.
Industry responses to these problems have been less than satisfactory. For example, one response has been to fill the voids or interstices at the base of the bearing housing prior to placing the housing in service. In one known approach, the entire base of the housing is overmolded with an elastomeric or thermoplastic elastomer filler in an attempt to cover the voids and cavities. However, this solution provides a product which is non-uniform in appearance, and which requires additional tooling and manufacturing processes, adding to the cost of the final product.
There is a need, therefore, for an improved polymeric bearing housing which does not suffer from the drawbacks described above. In particular, there is a need for a bearing housing which can be used in applications where environmental or health conditions require superior resistance to corrosion, while inhibiting the proliferation of microorganisms.
The invention provides an innovative polymeric bearing housing and a method for making such a housing designed to respond to these needs. The housing may be constructed in a variety of conventional styles, including pillow blocks, tapped base pillow blocks, two and four bolt flanged models, take-up frame models, and so forth. All of the models are molded from a polymeric material which can be properly formulated to provide the requisite mechanical integrity, while providing features inhibiting growth of microbes. Specifically, in a preferred embodiment an admixture of the polymeric material and an antimicrobial agent is formed prior to molding. The resulting structure thereby inherently inhibits the proliferation of microbes on and about the bearing housing. In accordance with another preferred embodiment, a foaming agent is added to the polymeric material to create a molded structure having varying densities throughout. Specifically, regions of higher density are formed near surfaces of the housing, while structural foam regions comprise the interior of the housing. Conventional structural ribs in a lower portion of the housing are thereby made unnecessary. The housing therefore includes a substantially planar support base which can be mounted on a machine frame with substantially no interstices between the housing and the machine frame.
In a preferred embodiment, the base material from which the bearing housing is made has a light or white color to provide strong contrast with potentially contaminating substances, such as in food and beverage applications. Moreover, for such applications the base polymeric material and the other components added to the material all preferably comply with U.S. Food and Drug Administration standards, making the housing suitable for use on and around food, beverage, pharmaceutical and similar products.
Thus, in accordance with the first aspect of the invention, a bearing housing comprises a unitary body made of a moldable polymeric material. The body includes a bearing insert support portion configured to receive and support the bearing insert. The body also includes a support base configured to receive and cooperate with fasteners to secure the bearing housing to a substantially planar machine surface. The support base has a mounting surface extending substantially in a plane. Thus, the housing may be installed on a planar machine frame with no interstices formed between the body and the frame where moisture or other debris or fluids can collect.
In accordance with another aspect of the invention, a support housing is provided for a bearing insert of the type including an inner race, an outer race, and an plurality of bearing elements disposed therebetween. A support housing comprises a bearing insert support portion and an attachment portion. The bearing insert support portion is configured to receive and support the bearing insert. The attachment portion is formed integral with the bearing insert support portion and includes a plurality of apertures configured to receive fasteners for securing the support housing to a machine support surface. The bearing insert support portion and the attachment portion both comprise an antimicrobial agent or component for inhibiting growth of microorganisms. In a particularly advantageous arrangement, the bearing insert support portion and the attachment portion are made of an admixture of a moldable polymeric material and the antimicrobial agent.
In accordance with another aspect of the invention, a method is provided for manufacturing a housing for a bearing insert. The housing comprises a bearing insert support portion configured to receive and support the bearing insert, and a mounting portion integral with the bearing insert support portion and configured for securing the housing to a machine frame. In accordance with the method, an admixture of a moldable polymeric material and an antimicrobial agent is formed. The admixture is injected into a mold to integrally form the bearing insert support portion and the attachment portion. The housing is then allowed to partially or completely cure and is removed from the mold. In a preferred embodiment, temperatures of surfaces of the mold are controlled during the molding and curing steps to form a substantially closed skin on the housing.
In another preferred method for manufacturing a bearing housing, an admixture of a moldable polymeric material and a foaming agent is formed. The admixture is injected into a mold to integrally form the support portion and the mounting portion of the bearing housing. A parameter of the mold is controlled to form boundary regions adjacent to surfaces of the housing, and internal regions. The boundary regions have a somewhat higher density than the internal regions. The housing is then at least partially cured and subsequently removed from the mold.